1. Field of the Invention
The invention relates to digital data communication systems. More particularly, the invention relates to a digital data communication system which transmits multiple bits per data symbol.
2. Related Art
Conventional digital communication systems use two levels of voltage or current to indicate the state of the transmission bit. The presence or absence of a voltage or a current represents a logical one or a logical zero. Typically, once a connection is established, data communication occurs at a fixed bit rate.
Conventional digital communications systems utilize a fixed size buffer. In such a system, data to be transmitted arrives at an input buffer. The data is clocked out of the input buffer at the fixed bit rate of the communication link until the buffer is empty. The rate of arrival of the data to the input buffer is a function of the application. However, a problem occurs if the data arrives more quickly than the data is clocked out because the input buffer becomes filled and may overflow, thereby resulting in a loss of data due to the overflow. Such a situation is referred to as a data bottleneck and typically is caused by applications which require intensive data throughput (also called "bursty communications"). Typically, a large buffer memory size is used to minimize data bottlenecks and thereby accommodate bursty communications. However, the cost of memory typically increases as the size of memory increases.